Cytochrome c

The significance of cytochrome c redistribution during the subcellular fractionation of rat liver

1. The redistribution of mitochondrial cytochrome c during homogenization and subcellular fractionation of the liver was studied. Chromatographically homogeneous (14)C-labelled cytochrome c was added in different amounts to liver suspensions immediately before homogenization and the adsorption of radioactivity was determined in cytochrome c fractions extracted at pH4.0, first with water and then with 0.15m-sodium chloride. 2. The soluble cytochrome c remaining in the cell sap after subcellular fractionation was 7% of the calculated amount of cytochrome c passing through a soluble form during the whole process. The total amount of cytochrome c released in a soluble form and subsequently redistributed was 25-30% of the total liver cytochrome c. 3. In the standard microsomal fraction the cytochrome c extracted with water originated entirely from redistribution whereas that extracted with 0.15m-sodium chloride was 80% endogenous. In the mitochondrial fraction both cytochrome c pools were truly endogenous, so that practically none of the mitochondrial cytochrome c released to the soluble cell sap was readsorbed by the mitochondria. 4. These results support our former hypothesis that the cytochrome c extracted with 0.15m-sodium chloride at pH4.0 from the standard microsomes represents the cytochrome c newly synthesized in situ, since it does not originate from redistribution. However, the microsomal pool extracted with water cannot be an intermediate in the postulated transfer of cytochrome c from the microsomal particles to the mitochondria, since this pool arises from redistribution of mitochondrial cytochrome c.

Chromatography of oxidized and reduced cytochrome c on carboxymethylcellulose

1. Cytochrome c was isolated from horse heart by a chromatographic method. 2. Oxidized and reduced cytochrome c were chromatographed on CM-cellulose that was in equilibrium with several buffer systems of constant composition at pH values of 8.4, 6.75 and 4.9. 3. Separation was better at the higher pH values; the oxidized form was retarded more than twice as much as the reduced form, though they differed by only a single charge. 4. Self-competition between cytochrome molecules is suggested to account for the peak distortion observed at high loads (above 20mum protein concentration).

Immunological time scale for hominid evolution

Several workers have observed that there is an extremely close immunological resemblance between the serum albumins of apes and man. Our studies with the quantitative micro-complement fixation method confirm this observation. To explain the closeness of the resemblance, previous workers suggested that there has been a slowing down of albumin evolution since the time of divergence of apes and man. Recent evidence, however, indicates that the albumin molecule has evolved at a steady rate. Hence, we suggest that apes and man have a more recent common ancestry than is usually supposed. Our calculations lead to the suggestion that, if man and Old World monkeys last shared a common ancestor 30 million years ago, then man and African apes shared a common ancestor 5 million years ago, that is, in the Pliocene era.

Subcellular distribution of cytochrome c in rat liver. Methods for its extraction and purification

1. A method for the extraction and purification of cytochrome c from rat liver is described. The method depends on multiple chromatography on Amberlite IRC-50 with elution with ammonium phosphate buffers of differing ionic composition and pH, interspersed with gel filtration with Sephadex G-25. Conditions leading to denaturation are avoided and the product is chromatographically pure. 2. The method may be used for the quantitative analysis of cytochrome c either in unfractionated liver or in subcellular fractions. 3. Two pools of cytochrome c were detected, one extractable at pH4.0 with distilled water and the other extracted from the residues of the first extraction with 0.15m-sodium chloride. 4. For subcellular distribution studies the liver was homogenized in 0.3m-sucrose and a nuclear fraction (washed thoroughly to remove trapped mitochondria), a mitochondrial fraction, a heavy microsomal fraction, a standard microsomal fraction and the cell sap were isolated. The mitochondrial fraction was subfractionated further by density-gradient centrifugation. Each fraction was analysed for protein, RNA, DNA, succinate-neotetrazolium oxidoreductase and glucose 6-phosphatase. 5. A total of 123mug. of cytochrome c was obtained/g. wet wt. of rat liver. 6. Values for the percentage subcellular distribution of cytochrome c are: nuclear fraction, 24.4; mitochondrial fraction, 57.2; heavy microsomal fraction, 5.2; standard microsomal fraction, 10.6; cell sap, 2.7. 7. Three out of the eight mitochondrial subfractions separated by gradient centrifugation contained 76% of the cytochrome c and 85% of the succinate-neotetrazolium oxidoreductase present in the mitochondrial fraction. 8. In unfractionated liver 94% of the cytochrome c was extracted at pH4.0 with water whereas in most of the subcellular fractions the corresponding value was approx. 75-80%.

Oxygenation properties of snake hemoglobin

Natrix taxispilota hemoglobin has a very high oxygen affinity which depends upon pH in an unusual manner. The oxygen affinity increases slightly upon protein dilution, but the pK's of the Bohr groups are unchanged. Oxidation promotes hemoglobin polymerization, which can be inhibited by prior treatment with iodoacetamide. Reaction with iodoacetamide also causes a slight increase in the oxygen affinity, no change in the pK's of the Bohr groups, and a drastic reduction in heme-heme interaction.

A Mössbauer study of ferri- and ferrocytochrome c

The Mössbauer spectra of horse heart ferri- and ferrocytochrome c were obtained at room temperature using lyophilized powders. The Mössbauer data indicate that the iron in both lyophilized samples is in a low-spin state. The high quadrupole splittings suggest that the iron atom is in an asymmetric ligand field. Upon reduction the asymmetry increases, suggesting a change in the bonding between the protein moieties and the iron atom.